The prior art of airspeed measurement is dominated for more than fifty years by pressure responsive probes based on pitot-static tubes and similar pneumatic devices, singly or in multiple arrangements. Notable are various multi-ported cylindrical and spherical probes as well as multi-dimensional "cobra" and "claw" probes, and the like. A combination vane and pressure difference "Air Speed And Attitude Probe" is disclosed by U.S. Pat. No. 4,184,149 that uses electromechanical and pneumatic sensors. A multi-ported differential pressure probe system for measuring air stream characteristics, static pressure, and turbulence intensity is disclosed by U.S. Pat. No. 5,233,865.
Electrical airspeed measurement by thermal anemometry variations has emphasized low speed measurements, generally lower than routine aircraft operating airspeeds. The use of heated metal film strips and rings capable of operating at aircraft cruising airspeeds is disclosed by U.S. Pat. No. 3,352,154. Segmented heated films on a sensing body to measure airflow speed and direction is disclosed by U.S. Pat. No. 3,604,261. U.S. Pat. No. 3,677,085 discloses a spaced apart hot wire pair, embedded in a support, that measures in-line bidirectional flow in a pipe. A pair of heated sensing elements, with a figure-eight cross-section, is disclosed by U.S. Pat. No. 3,900,819, where free-field flow is measured in the plane containing both sensing element axes.
A more up-to-date disclosure of the use of a single heated cylinder for airspeed measurement is outlined in the specification for U.S. Pat. No. 5,639,964. It is taught that instantaneous airspeed and a planar component of longitudinal airspeed can be selected from a composite airspeed signal by appropriate low-pass and band-pass filtering. Paired hot film multi-component thermal anemometry is taught by U.S. Pat. Nos. 5,357,795, 5,218,865, and prior patents. Construction of a wire wound sensing element for use in air flow metering is taught by U.S. Pat. No. 4,513,615.
Most anemometers intended for meteorological and helicopter airspeed measurements are inappropriate for use on aircraft because of their relative fragility and inability to withstand continuous airstream punishment by rain and frozen precipitation, and their general design approach which focuses on open free-field measurements in two-dimensional and, in some cases, three-dimensional space, rather than the measurement of dominant flow from one direction as in the case of an aircraft airspeed sensor.
It is, therefore, an object of the instant invention to provide a rugged fast response aircraft airspeed and airspeed cross-component transducer capable of direct sensing of instantaneous airspeed as well as turbulence components.